Relays are used in a variety of control functions in manufacturing operations, such as controlling machines, motors, sequences, etc. However, it is necessary to operate these relays by a safe and reliable control circuit. Particularly important is the isolation of the control circuitry for the relay from the power circuits that are controlled by the relay contacts. If such isolation is not properly achieved, shorts or other electrical malfunctions in the circuits can endanger, and even kill, workmen using machinery equipped with such control relays.
Electrical isolation is not the only concern since improper operation of the control relay may also place the operator of such machinery in jeopardy, as well as endanger the equipment itself.
To increase reliability higher voltage and current have often been used in the relay control circuits leading to a situation whereby direct sensing of conductive parts for relay control can lead to etching, as well as increase the danger of electrical shock.
The current invention solves the above problems with a differential impedance circuit that provides full isolation from the relay power circuits and exceptional reliability in the control circuits for operating the relay.
Not only does the instant invention solve the above problems, but it does so economically.
By using what might be characteristically described as "differential impedance switching" employing a floating voltage to control the gate of a silicon controlled rectifier or similar switching device the above objects can be realized. While in retrospect the circuits of the invention appear to be simple, their function and operation is a unique departure from prior art arrangements. The specialized circuit ensures positive and consistent operations of the relay with voltage potentials in the control circuit of 10 volts or less.
There are many applications for this very versatile device. The solid state input circuit has high impedance (10K ohms), low energy (Open Circuit Voltage (OCV) of .+-.10 volts peak). The relay outputs offer flexibility, total circuit isolation and use of indestructible DPDT relays, capable of driving solenoids, large motor, starters or small motors directly. These characteristics combined with the low price and ease of installation makes this invention the logical choice to solve thousands of control problems.
The novel unit is a control switching device, actuated by the touch of its low voltage high impedance input lead (probe) to ground potential. The acquisition and logic functions are of a high speed solid state design and provide either momentary or latching action. The relay output contacts can yield maximum ruggedness and flexibility in all applications. The unit can also be designed to plug into a standard 11-blade relay socket, and has no adjustments or controls. It is maintenance free and is powered directly by the 120-volt, 60 Hz line so it requires no separate power supply, rectifiers, or transformer. It is capable of a compact design which permits its mounting in existing control panels or near its point of use.